Ch7. Chromosome Mutation Variation in Number and Arrangement. Although most members of diploid species normally contain precisely two haploid chromosome sets, many known cases vary from this pattern.
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Although most members of diploid species normally contain precisely two haploid chromosome sets, many known cases vary from this pattern.
Modifications include a change in the total number of chromosomes, and changes of chromosomal structures, the deletion or duplication of genes or segments of a chromosome, and rearrangements of the genetic material either within or among chromosomes.
Euploidy(整倍体): monoploidy and polyploidy
polyploidy :Autopolyploidy(同源) Allopolyploids(异源)
Aneuploidy(非整倍体): loss 2n- 1 or more and add 2n+1 or more of the whole set of chromosomes
Cri-du-Chat animal species is at first quite puzzling, since at least a single copy of every gene is present in the remaining homolog. Syndrome
In humans, autosomal monosomy has not been reported beyond birth. There are, however, examples of survivors where only part of one chromosome is lost. These cases are sometimes referred to as segmental deletions.
One such case was first reported by Jerome LeJeune in 1963 when he described the clinical symptoms of the cri-du-chat (cry of the cat) syndrome. This syndrome is associated with the loss of part of the short arm of chromosome 5 (Figure 7-2). of
Thus, the genetic constitution may be designated as 46,5p-, meaning that such an individual has all 46 chromosomes but that some
7.4 Trisomy animal species is at first quite puzzling, since at least a single copy of every gene is present in the remaining homolog.
A1A2a 3 (A1A2 a3 A1a3 A2 ) X 2 (a2A1 A2 ) x 2 animal species is at first quite puzzling, since at least a single copy of every gene is present in the remaining homolog.
例如： animal species is at first quite puzzling, since at least a single copy of every gene is present in the remaining homolog. P a/a x +/+/+
F1 a/+/+ 与 a/a测交
配子 2/6 a/+ 2/6 + 1/6 +/+ 1/6 a
eyeless female ( animal species is at first quite puzzling, since at least a single copy of every gene is present in the remaining homolog. ey ey) and a haplo-IV normal eye male (ey+).
PATAU animal species is at first quite puzzling, since at least a single copy of every gene is present in the remaining homolog. syndrome = trisomy 13
- facial defects, polydactyly, heart defects, die within a few months of birth
EDWARDS syndrome = trisomy 18
- small + muliple defects, usually die in first year of life
DOWN syndrome = trisomy 21
FIGURE animal species is at first quite puzzling, since at least a single copy of every gene is present in the remaining homolog. 7-5
The karyotype and phenotypic depiction of an infantwith Patau syndrome, where three members of the D-group chromosome 13 are present, creating the 47,13+ condition.
FIGURE 7 animal species is at first quite puzzling, since at least a single copy of every gene is present in the remaining homolog. —4 Incidence of Down syndrome births contrasted with maternal age.
FIGURE 7-6 composition. This can occur Contrasting chromosome origins of an autopolyploid versus an allopolyploid karyotype.
FIGURE 7-7 composition. This can occur The potential involvement of colchicine(秋水仙素) in doubling the chromosome number, as occurs during the production of an autotetraploid. Two pairs of homologous chromosomes are followed. While each chromosome has replicated its DNA earlier during interphase, the chromosomes do not appear as double structures until late prophase. When anaphase fails to occur normally, the chromosome number doubles if the cell reenters interphase.
FIGURE 7-9 composition. This can occur The origin and propagation of an amphidiploid(双二倍体).
Species I contains genome A consisting of three distinct chromosomes, a,, a2, and a3.
Species 2 contains genome 6 consisting of two distinct chromosomes, b1 and b2.
Following fertilization between members of the two species and chromosome doubling, a fertile amphidiploid containing two complete diploid genomes (AABB) is formed.
（ are larger than their diploid counterpart. 1）概念：同一细胞或个体染色体数目的加倍
Genotype Gamete Ratio Phenotypes are larger than their diploid counterpart.
三显性 AAAa 1AA：1Aa all A
二显性 AAaa 1AA：4Aa：1aa 35A：1a
单显性 Aaaa 1Aa：1aa 3A：1a
种 学名 亚种 染色体数
二倍体小麦 滔氏麦草 T tauschii 14
斯氏麦草 T searsii 14
一粒小麦 T monocum 野生种 14
四倍体小麦 二粒小麦 T dicocum 28
提莫非维 T timopheari 28
茹科夫斯基 T zhukovskyi 42
普通小麦 T aestivum 许多种 42
Spartinia final symbol X. Speciation
Wild potato (2n=24)Cultivated Potato (2n=48)
Wild Cotton (2n=26)Cultivated Cotton (2n=52)
Dahlia (2n=32)Garden Dahlia (2n=64)
Wild Tobacco (2n=24)Cultivated Tobacco (2n=48)
For some plant species a series of successive ploidy levels are seen.
Allopolyploids established within 100 years because of its vigorous growth.
The New World cotton species Gossypium hirsutum has a 2n chromosome number of 52. The Old World species G. thurberiand G. herbaceum each have a 2n number of 26. Hybrids between these species show the following chromosome pairing arrangements at meiosis:
The second general class of chromosome aberrations includes structural changes that delete, add, or rearrange substantial portions of one or more chromosomes
Vitality by DELETIONS染色体结构的变异，一般认为，来自于染色体或染色单体的断裂
Cell or chromosome behavior DELETIONS 染色体结构的变异，一般认为，来自于染色体或染色单体的断裂
Genetic effect by DELETIONS 染色体结构的变异，一般认为，来自于染色体或染色单体的断裂
DELETIONS染色体结构的变异，一般认为，来自于染色体或染色单体的断裂 deletions & human disease
FIGURE 7-11 The origin of duplicated and deficient regions of chromosomes as a result of unequal crossing over. The tetrad on the left is mispaired during synapsis. A single crossover between chromatids 2 and 3 results in deficient and duplicated chromosomal regions (see chromosomes 2 and 3, respectively, on the right).The two chromosomes uninvolved in the crossover event remain normal in their gene sequence and content
segments on homologue
The 染色体结构的变异，一般认为，来自于染色体或染色单体的断裂Bar Mutation in Drosophila
Gene Redundancy and Amplification染色体结构的变异，一般认为，来自于染色体或染色单体的断裂—Ribosomal RNA Genes
Although many gene products are not needed in every cell of an organism, other gene products are known to be essential components of all cells. For example, ribosomal RNA mustbe present in abundance in order to support protein synthesis. The more metabolically active a cell is, the higher is the demand for this molecule. We might hypothesize that a single copy of the gene encoding rRNA is inadequate in many cells. Studies using the technique of molecular hybridization, which allows the determination of the percentage of the genome coding for specific RNA sequences, show that our hypothesis is correct! Indeed, multiple copies of genes code for rRNA. Such DNA is called rDNA, and the general phenomenon is called gene redundancy.
The Role of Gene Duplication in Evolution染色体结构的变异，一般认为，来自于染色体或染色单体的断裂
A B C D E F G H
A B F E D C G H
Consequences Inversions of Inversions During Gamete染色体结构的变异，一般认为，来自于染色体或染色单体的断裂
D / +
D+/++ × +Gl/++
++/++ D+/++ D+/+G l ++/+Gl
D+/D+ D+/+Gl +Gl/+Gl
Cy + Cy +
+ A + A
Cy + Cy + + A
Cy + + A + A
易位造成花斑型位置效应（这种非同源染色体上的基因在形成配子时相互不能自由组合的现象称为假连锁。variegated type of position effect）
（Activator-Dis sociation system）
Translocations in Humans:白两种颜色的体细胞镶嵌的斑驳色眼，故又名为斑驳型位置效应。其遗传机制在于红眼等位基因Familial Down Syndrome
7.11 Fragile two copies of chromosome 21: a normal chromosome and a second copy translocated to chromosome 14. When such a gamete is fertilized by a standard haploid gamete, the resulting zygote has 46 chromosomes but three copies of chromosome 21. These individuals exhibit Down syndrome. Other potential surviving offspring contain either the standard diploid genome (without a translocation) or the balanced translocation like the parent. Both cases result in normal individuals. Knowledge of translocations has allowed geneticists to resolve the seeming 脆性 Sites in Humans
Fragile X Syndrome (Martin-Bell Syndrome strong association was subsequently shown to exist between one of the sites and a form of mental retardation.
Fragile Sites and Cancer expansion has not yet been established, several factors are known that influence the instability. Most significant is the observation that expansion from the carrier status (55-200 repeats) to the syndrome status (over 200 repeats) occurs during the transmission of the gene by the maternal parent, but not by the paternal parent. Furthermore, several reports suggest that male offspring are more likely to receive the increased repeat size leading to the syndrome than are female offspring. Obviously, we have much to learn about the genetic basis of instability and expansion of DNA sequences